As domino already explained, use for 1) and 2) the IP: 192.168.1.102
Maildir vs. Mbox:
These are two email storage formats. Maildir means, that every mail is stored in a separate file inside the maildir directory. Mbox means, that all emails are stored in one large file, the format of this file is named mbox.
How to decide if you need Mbox / Maildir:
ISPConfig supports both formats, but most POP3 and IMAP Daemons support only MBox or Maildir, so you have to chose the mail storage format in ISPConfig that is supported by your POP3 and IMAP Daemon.
For example, courier is one of the few Daemons that support Mbox and Maildir, in this case i recommend to use Maildir because it is more robust and scales better than mbox format.
The default format in Fedora and SuSe is Mbox (please correct me if i'am wrong).